The importance of styrene as a large volume organic commodity has stimulated increasing efforts to develop new and improved methods for efficient synthesis of the compound.
In many of the processes contemplated for styrene synthesis, vinylcyclohexene or ethylbenzene function as starting materials or as key intermediates.
U.S. Pat. No. 2,976,331 describes a method for simultaneously effecting the catalytic dehydrogenation of a naphthenic hydrocarbon to an aromatic and the catalytic hydrogenation of an olefin to paraffins which involves contacting a naphthene/olefin mixture at 350.degree.-850.degree. F. with a crystalline metallo-alumino-silicate catalyst having uniform pores of 10-13 angstroms.
U.S. Pat. No. 3,502,736 describes a method for the oxidative dehydrogenation of a nonaromatic cyclic hydrocarbon having at least one unsaturated bond in a side chain, which method consists of contacting the said cyclic hydrocarbon in the presence of oxygen with a catalyst consisting of palladium oxyhydrate. In Example 1, the conversion rate of vinylcyclohexene is 86.8 percent, and the selectivity to styrene is 91.3 percent.
U.S. Pat. No. 3,903,185 describes a dehydrogenation process which is reported to be capable of converting vinylcyclohexene to ethylbenzene with a 96.6 percent selectivity. The process parameters include a 350.degree.-450.degree. C. temperature, a 2.5-30 atmospheres pressure, 0.2-20 m.sup.3 of hydrogen/kg of vinylcyclohexene, and a catalyst containing metal elements selected from subgroups VI-VIII of the periodic table.
U.S. Pat. No. 4,163,761 describes a liquid phase process which involves converting vinylcyclohexene to styrene at a temperature of 170.degree.-360.degree. C. in the presence of a nitro compound and a copper chromite catalyst. The Example 1 data indicate a 19.2 percent selectivity of vinylcyclohexene to styrene, and a 7.5 percent selectivity to ethylbenzene.
U.S. Pat. No. 4,165,441 describes a vapor phase process for converting vinylcyclohexene to styrene which involves contacting vinylcyclohexene with oxygen in the presence of a tin-antimony oxide catalyst. A typical result in Table 1 indicates 82.4 percent vinylcyclohexene conversion, and a product selectivity of 58.9 percent styrene and 6 percent ethylbenzene, respectively.
Other United States patents of general interest with respect to dehydrogenation technology include U.S. Pat. Nos. 2,392,960; 2,404,104; 2,438,041; 2,560,329; 3,236,903; 3,409,690; 3,437,703; 3,511,885; and references cited therein.
The prior art vinylcyclohexene dehydrogenation processes characteristically produce mixtures of styrene and ethylbenzene, and usually only partial conversions are achieved. In many cases good conversion rates are counterbalanced by short-lived catalyst activity. Further, high temperatures and pressures cause cracking and isomerization side reactions. Objectional amounts of benzene, toluene and xylene are formed, and these are difficult to separate from ethylbenzene. Some processes require the use of hydrogen, which adversely affects the economics of a process.
Accordingly, it is an object of this invention to provide a process which is adapted to convert vinylcyclohexene to ethylbenzene under relatively mild conditions with a conversion of at least 90 percent and a selectivity of at least 95 percent.
It is a further object of this invention to provide a dehydrogenation catalyst which exhibits long term activity under continuous operating conditions, and which is highly selective for vinylcyclohexene conversion to ethylbenzene.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.